Conventional galvanic dry cells for use in flashlights, toys or other sundry devices generally comprise a cylindrical container, such as a zinc anode can, with a depolarizer mix filling most of the container and having a carbon rod in the center which functions as the current collector for the depolarizer mix. The cells are generally sealed by inserting a support washer over the cathode depolarizer mix and then dispensing molten asphalt onto the washer thereby providing an asphalt seal for the cells while also providing an airspace above the depolarizer mix and below the asphalt seal to accommodate the discharge gases and exudate of the cells.
Although asphalt seals have been employed with some success in sealing galvanic dry cells, they do have a number of drawbacks or disadvantages. For example, several assembly procedures are required such as placing a support washer down into the cell, pouring an asphaltic pitch onto the support washer, placing a vent washer on top of the asphaltic pitch and then finally placing a terminal cap on top of the cell and locking it in place. The vent washer can be used to prevent the terminal cap from becoming embedded in the pitch which could possibly result in forming a gastight seal which could prevent venting. In addition, it is possible that the inside surface of the container could become dirty due to mercury contamination prior to dispensing the asphaltic pitch. This could result in a pseudo-seal which, over a period of time, could eventually lead to moisture loss from the cell and/or oxygen ingress to the cell because of insufficient adhesion of the pitch to the can or container. It is also possible that during the heating of the asphalt pitch to cause a meniscus to form at the can-asphalt interface, pin holes may form in the pitch as a result of expansion of the air in the void volume below the support washer which would allow moisture loss and/or oxygen ingress to the cell. Another disadvantage in the use of conventional asphalt seals is that they physically take up a relatively large space in the cell thereby limiting the size of the airspace into which the reaction products of the cells can discharge.
In the above-described cells, the venting of the gases from within the cell can take place through a porous current collector such as a carbon rod or the like. Although a properly prepared asphalt seal will effectively minimize electrolyte or moisture loss through evaporation and minimize air or oxygen ingress to the cells, the assembly and quality control techniques required to insure good seals are rather expensive and time consuming.
Finished cells that do not meet the minimum quality standards for one reason or another are usually disassembled or detubed so that the raw cell components can be reused. However, in conventional constructions where the container is adhered to a jacket, recovery of the raw cell components is messy and expensive. Furthermore, when a top centering seal washer is employed as part of the finished cell, the detubing operation (removal of the outer jacket) may disturb this centering washer which in turn may cause the depolarizer mix contact to be somewhat loosened which could result in loss of amperage.
U.S. Pat. No. 3,967,977 discloses a closure for galvanic cells having a centrally disposed tubular neck adapted to be snugly slid over and adhesively secured to the current collector of the cell and having a peripherally disposed tubular skirt adapted to be snugly slid on and adhesively secured to the upper rim of the cell's container thereby providing a seal for the cell. The only venting in this type of cell construction is through the wall of the carbon electrode. In some cell systems that develop a relatively high amount of spew and/or gas, this cell construction may be inadequate.
An object of the present invention is to provide a one piece closure for a dry cell which provides maximum airspace above the depolarizer mix of the cell and below the closure.
Another object of the present invention is to provide a thin molded plastic cover in conjunction with an undercoating of a soft sealant, such as asphalt, as a closure for a galvanic cell which produces a good seal and venting means while avoiding cell heating resulting from in situ asphalt pouring that is generally necessary when using conventional asphalt sub seal techniques.
Another object of the present invention is to provide a thin closure for a galvanic dry cell having a top surface contour fabricated to substantially conform to the bottom surface contour of a metal terminal cap of the cell so as to provide a maximum airspace above the depolarizer mix of the cell and below the closure.
Another object of the present invention is to provide an easy and inexpensive method for assembling a closure onto the container of a cell so as to seal the container.
The foregoing and additional objects of this invention will become more fully apparent from the following description and accompanying drawings.